/* =============================================================
 * Your Grandmother's guide to Algorithms
 * =============================================================
 *
 * Copyright (c) 2007, Saverio Miroddi
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 * 
 *     * Redistributions of source code must retain the above copyright notice,
 *       this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright 
 *       notice, this list of conditions and the following disclaimer in the 
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the SaverioMiroddiSoftware nor the names of its 
 *       contributors may be used to endorse or promote products derived from 
 *       this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER 
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *  
 * ---------------------------
 * AbstractAlgo.java
 * ---------------------------
 *
 */
package algos;

import dbobjects.Condition;
import dbobjects.tables.Table;

/**
 * In all join algorithms, for implementing RIGHT OUTER joins, just reverse
 * left-right in the constructor (this.leftTable = rightTable and
 * this.rightTable = leftTable), then re-reverse the records during
 * assembleJoinRow();
 *
 * @author Saverio Miroddi
 */
abstract class AbstractAlgo implements IAlgo {
	protected Table leftTable, rightTable;
	protected Condition cond;
	protected int type;
	
	protected String[] currRow;

	/** true when the right table has been iterated completely */
	protected boolean advanceLeft;
	
	/** true when during after the complete iteration of the right table,
	 * at least one row has been found */
	protected boolean foundRightRow;

	AbstractAlgo(Table leftTable, Table rightTable, Condition cond, int type) {
		this.leftTable = leftTable; 
		this.rightTable = rightTable;
		this.cond = cond;
		this.type = type;
		
		advanceLeft = true;
		foundRightRow = false;
	}
	
//	In Java, we must keep track of the outer loop iterator, because we don't
//	want to advance it every time we enter the method. 
//	Python language has yield() function, which makes the looping very simple.
	
	protected boolean leftOuterLoop() {
		if (advanceLeft) {
			if (leftTable.next()) {
				rightTable.beforeFirst();
				foundRightRow = false;
			}
			else {
				currRow = null;
				return false;
			}
		}
		
		return true;
	}
	
	protected boolean rightInnerLoop() {
		if (rightTable.next()) {
			advanceLeft = false;
			return true;
		}
		else {
			advanceLeft = true;
			return false;
		}
	}
	
	public String[] getCurrentRow() {
		return currRow;
	}
}